1. Field of the Invention
The present invention relates to a pressure control valve for controlling a pressure in a fuel tank, such as a fuel tank of an automotive vehicle.
2. Description of Related Art
A pressure control valve is disposed in a passage connecting a fuel tank of an automotive vehicle to an atmospheric pressure to prevent excessive negative pressure from being developed in the fuel tank. The atmospheric pressure is supplied, for example, from a drain port of a canister that temporarily holds fuel vapor generated in the fuel tank and suppresses fuel vapor exhaust from the fuel tank.
An example of such a pressure control valve is disclosed in JP-A-8-121619. The control valve includes a wall separating a valve chamber from a canister port and a valve body disposed in the valve chamber. A through-hole formed in the separating wall is opened or closed by the valve body according to a difference between the fuel tank pressure and an atmospheric pressure. The valve body is biased by a spring in a direction to close the through-hole. The valve chamber always communicates with a fuel tank port, and a canister inner pressure is applied to a front surface of the valve body while a fuel tank inner pressure is applied to a back surface of the valve body. When the fuel tank inner pressure decreases to a predetermined level, the valve body opens the through-hole to introduce atmospheric pressure into the fuel tank. The valve body is formed by connecting a dish-shaped metallic member to a rubber disc. A circular lip portion is formed on the rubber disc to tightly close the through-hole.
Another example of the valve device for preventing the fuel tank pressure from becoming excessively negative is disclosed in JP-A-6-50447. In this device, a hole communicating with atmosphere is formed in a top plate of a fuel tank cap, and the hole is usually closed by a valve body disposed inside the top plate. The valve body is biased by a spring in a direction to close the hole. When the fuel tank pressure decreases to a predetermined level, the valve body opens the hole against the biasing force of the spring to introduce the atmospheric pressure into the fuel tank. The valve body is composed of a cup-shaped rubber member having a circular sealing lip to tightly close the hole.
There is a problem in both of the conventional pressure control valves. When the atmospheric pressure is once introduced into the fuel tank through the open valve, the atmospheric pressure is immediately applied to the inner surface of the valve body. Accordingly, the open valve is instantly closed, and the negative pressure quickly develops in the fuel tank to open the valve again. This results in a vibrating operation of the valve between its closed and open positions with a short cyclic period. The vibrating operation of the valve generates vibrating noise.